Serotonergic antidepressants are clearly effective for premenstrual syndrome (PMS). This study compares short-term treatment (4 months) and long-term treatment (12 months) with sertraline to determine how long medication should be continued after achieving a good response, how soon symptoms return after stopping medication, and whether symptoms are further improved with long-term treatment. Multiple hypotheses include the following: The percent of relapsed subjects is greater with short-term treatment; relapse is swifter with short-term treatment; relapsed subjects improve swiftly when returned to medication; patient satisfactions and quality of life are more improved with long-term treatment.